


About a Beta

by Anonymous



Category: The 100 (TV)
Genre: Alpha/Beta/Omega Dynamics, Beta!Octavia, Blakecest - Freeform, Eventual Bellamy/O/Clarke, F/M, Knotting, Loss of Control, Loss of Virginity, Oral Knotting, Oral Sex, Rough Sex, Sibling Incest, alpha!bellamy, dubconish, eventual OT3, lots of smut, mentions of other kinks, mild choking
Language: English
Status: Completed
Published: 2019-11-12
Updated: 2019-11-18
Packaged: 2021-01-29 14:07:22
Rating: Explicit
Warnings: Underage
Chapters: 2
Words: 3,534
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21411415
Author URL: https://archiveofourown.org/
Summary: Bellamy keeps her safe, so Octavia keeps him sane.
Relationships: Bellamy Blake/Octavia Blake
Comments: 12
Kudos: 80
Collections: Anonymous, The 100 WTFluff





	1. Chapter 1

**Author's Note:**

> Incest and Underage. Read beyond this at your own risk. Any rude comments will be reported and deleted.

Octavia was fifteen the first time it happened. Bellamy came home in a huff. She could tell from across the room that his body was buzzing as his hands kept busy running through his hair, over his face, grazing his neck as he stretched it- trying to relieve any tension he could.

“What’s wrong?” she asked, her eyes narrowing while Bellamy went rigid. Without a word, her brother walked to his bed and collapsed. 

“O, get to bed and cover your ears, please,” he said, his voice rough, “I need some time alone.” 

She knew well enough what that meant, “you caught a scent, didn’t you?” she asked eagerly, before she made her way over to him, and sat down, “Bell, you don’t have to hide.” 

“Octavia, please,” he pleaded, “I can’t talk right now... I have to- I'm gonna go crazy.” 

Octavia surveyed her brother as he stretched out and waited for her to leave. He didn’t know it, but the last few times he had done this, she watched from her spot under the floor. She saw everything, the way his hands gripped his cock, the way he pumped, twisted, and released his knot on himself. She listened to his growls, his panting- she even rubbed herself, as she silently took in the way his hips hurried to meet his fist’s movements. 

She thought about it all the time. When he wasn’t home, she would bury her face in his pillow and rub herself until she came hard, moaning as quietly as she possibly could. 

“Let me,” she whispered, leaning forward to set her hand on her brother’s cock.

_ “O,” _ he warned, eyes flashing at her dangerously, “you shouldn’t.”

“I want to,” she said, rubbing him lightly as she leaned forward, “please, big brother- I want to help you. You keep me safe, let me do this for you.” 

Bellamy stared at her blankly before his hand grabbed hers. For a moment, Octavia thought that he was going to push her away. Still, instead, he pressed her hand harder and against himself and began to grind against it, “you wanna help make your big brother come?” he asked, his eyes softening a little, “what a good little beta, being here for me.” 

Octavia couldn’t help but blush under his praise. After a minute, though, she leaned forward and unzipped his pants, “tell me if I need to do anything different. I’ve only read about it- and I watched you a couple of times.” 

At that, Bellamy’s pupils dilated as his gaze grew dark and his mouth dropped open, “you- you watch me?” 

“Does that bother you?” Octavia waited for him to swallow and shake his head before she took out his cock. As she ran her hand up and down his substantial length, she noticed his lower abs convulsing and could feel his pulse against her palm, “you’re so big.” 

“Octavia, I-” Bellamy began but lost his train of thought as she began to jerk him off. Octavia worked diligently and carefully as she tried to remember the few examples of this she had filed away in her mind. 

_ “Fuck, O,” _ he groaned as she smothered his precum over the tip of his cock. Pulling her hand away, she kept her eyes on his as she licked her palm, from her wrist to her fingertips, and began her work again. The man let out a moan as she sat up on her knees and lowered her mouth to his cock. 

After some awkward maneuvering and gentle encouragement from Bellamy, Octavia figured out a rhythm. She paid close attention to all of his noises, making sure to repeat anything that elicited a moan or groan from him. As she continued to suck him off, one of his hands found her hair, while Bellamy ran the other over her ass.

“God, O, you’re so good,” Bellamy said, his hand sliding up her dress, and under her ark-issued underwear, “I should have known you’d know what to do with that pretty little mouth of yours- you are a Blake after all.” 

Octavia hummed at his endearing compliment. After a moment, she let out a moan of her own as Bellamy’s fingers came up to play with her clit. By now, she was pumping him hard, taking breaks to let her jaw rest, and then going back for more. 

“Get up here, O,” Bellamy growled, and Octavia looked up to see his eyes completely black, “c’mon,” sitting back on her knees, she merely stared at Bellamy as he moved to undress her, “sit on my face.” 

She felt both turned on and somewhat embarrassed as her brother spread her pussy lips before him, “fuck, so beautiful,” he groaned before licking right into her. There was immediate electricity as Bellamy went to work ferociously, eating her out. Forgetting her task, O played with her tits as his tongue and thumb fucked into her, and his fingers pressed hard against her clit. Shaking from sensation, she came so hard she had to bite down on her hand to keep the noise down. 

As soon as her breath evened out, her lips were back around his large and pulsing alpha cock. O had to stretch her jaw as wide as possible as his knot grew. When it began to move up his shaft, Bellamy tried to stop her.

“Wait, you can't you'll hurt-” Bellamy began, but the words evaporated into loud, pleasurable groans as Octavia took his seed in her mouth and swallowed until there was not a drop left. 


	2. Chapter 2

**Summary for the Chapter:**

> When Bellamy finds himself in a rut- O convinces him to take out on her.

It becomes a habit. 

Every time Bellamy catches a scent, or another Alpha tries to challenge him, Bellamy buries his frustration and doesn’t do anything about it until he gets home. Most of the time, O helped out by giving him a hand or sucking him off. He’d given up on feeling guilty about it a long time ago- and now, it’s become a playful thing that he can tell she enjoys just as much as he does. 

For over a year, he drew the line at oral. He’d let O sit on his face, he’d get on his knees for her- he'd let her take his cock down her throat- he even let her rim him, while she pumped his knot out onto the bedsheets. Almost everything they had tried had been her idea- and it really shouldn’t surprise him that his sister had a filthy mind- after all, it seemed to run in the family. 

He had two rules: don't fuck and don’t kiss your baby sister. 

Maybe it was stupid, they both made each other come regularly... but there had to be some sort of boundaries... some sort of rules, right? 

Well, that worked out pretty well until Bellamy went into his first real rut. 

Usually, his mom got a hold of a shot for him- he needed to have one every few months, and it would keep his urges in check. Considering there were no Omegas that he responded to in the family quarters, Bellamy had almost no issue. And with Octavia helping him out, he forgot about the shot altogether. 

He forgot that is until his body so rudely reminded him. 

It started while he and the fellow cadets were patrolling Alpha Station. Chancellor Jaha, Marcus Kane, and Jake Griffin were discussing safety concerns regarding parts of the Ark that were off-limits but had been routinely broken into by some unknown youth. 

Truth be told, Bellamy couldn’t remember much of the conversation after a certain blonde Omega entered the room. 

By the looks of it, there were only two Alphas in the room- Bellamy and Mr. Griffin. 

Bellamy caught her scent and heat immediately rushed to his groin. With his mouth dry, and blood rushing in his ears, he stared the girl down. She had to be around O’s age. The scent was familiar and overwhelming. It had to be the scent he’d caught in the past. 

“Dad?” the girl said in a low and husky voice. She kept her eyes down, and Bellamy watched as her father checked in with her. 

“Are you okay, Clarke?” Mr. Griffin asked, his eyes flitting over his daughter. As soon as he took in her flushed face, the man looked around. For just a moment, Bellamy met his eyes. 

“I’m fine,” she whispered, leaning in and sharing something else with her father. 

“Okay kiddo,” Mr. Griffin said, “let your mom know I’ll be on my way in twenty minutes.” 

Clarke nodded and turned to walk away. Before she got too far away though, her father called her back over, “be careful, honey,” he warned. As if just catching on, Clarke nodded again and pulled her hair out of its tie- allowing her golden locks to cover up the scent glands on her neck. 

Bellamy tried not to stare as she walked past him, but when his eyes fell to her chest, he saw that her nipples were already peaked. For a brief moment, her eyes met his and Bellamy’s heightened sense smell picked up something else- _ the scent of arousal. _

Her breath stilled, and her eyes dropped before she rushed past the guards- likely off to go hide while she rode out the heat that an Alpha's presence just triggered. Bellamy was able to stay in the Chancellor’s office for another five minutes before he had to make up an excuse to leave. 

After making it clear that he was going to med (and not following Mr. Griffin’s daughter), Shumway let him go. Instead of going to med though, Bellamy walked right past the clinic, and almost ran home. As soon as he was through the door, he pulled off his vest and began to unbutton his shirt. 

“Bellamy?” Octavia’s voice met his ears, filled with concern as she got up and walked over to him, “are you okay?” 

“O,” he growled, already losing control, “I need you to move.” 

“What happened?” 

“The Omega- I was in the same room as her...” he said through gritted teeth, making his way to the closet and pulling out a little black bag of medication. With hands shaking, Bellamy plunged a clean syringe into the vial of medication and stabbed it into his leg promptly, “Octavia, get under the floor- you can’t come out for twenty-four hours.” 

“Bell, please... I can help you.” 

“_No, Octavia. _ I'll hurt you. I can’t do that.” 

“Bellamy, you haven’t hurt me-” 

“I also haven’t fucked you, O!” Bellamy yelled, the words coming out harsher than intended, “Octavia, you’re not an Omega. If I lose control, I could seriously hurt you.” 

“I can handle you,” she said, sounding wounded. 

“Just leave me alone... the shot will kick-in within a day or so.” 

She didn’t say a word as she sat on the edge of his mom’s bed. Already overheating, Bellamy’s clothes felt like flames against his skin. In a huff, he peeled his clothes off and laid above the covers in just his boxers. 

As heat spread through his body, Bellamy’s head felt heavy and his eyelids drooped. 

He woke sometime later, his body feeling warm and wound up. As his vision come into focus, Bellamy spotted O above him in the warm lamplight, her hands moving to wring out a washcloth. When the cool cloth hit his forehead, he let out a little moan. 

“Hey, you’re awake,” she said, smiling softly, “you’ve been burning up like crazy. Mom came by and uh, did that.” 

As O motioned, Bellamy followed the direction and saw exactly what their mother had done, “she tied me up?” 

“I told her she didn’t have to- you aren’t going to hurt me.” 

“You can’t know that O... this is safe, at least.” 

“Bellamy,” Octavia murmured as she let first her eyes, then her index finger, fall to his chest, “mom told me what happens when you get into a rut. Even with the shot... you won’t come down until you-” 

_ “Please- don’t tempt me,_” Bellamy begged, as his throat felt thick and strained. His head was spinning and his body was burning up, every time he moved against the ropes, every time the sheets grazed his skin or her fingers drew another circle, his arousal only intensified. Looking away, his body lurched forward against the ties and he was certain that the cooling feel of the water against his skin was the only thing keeping him from combusting. 

As if reading his mind, O leaned over to grab the cloth again- and just the scent of her over him had his mouth watering, and cock twitching in anticipation. Logically, he knew Octavia wasn’t an Omega, but his body still wanted her. Maybe they had gone down on one another a few too many times, or maybe it was just that his sister was beautiful, smart, and ignited something warm in him that engulfed his entire being. 

Instead of giving him more water, his sister kept silent as she laid down and set her head on Bellamy’s shoulder, “Bell, I love you, and I hate seeing you suffer,” she whispered. When he turned his face away from her, O caught his chin and brought him back, her eyes fierce and commanding- “Do you hear me, big brother? _ I don’t like seeing you suffer. __Your pain hurts me. _” 

Swallowing hard, Bellamy tried to figure out what to say- but all he could think of was, _"I love you, too."_

The admission came out as more of a plea and as O stared at him, Bellamy felt his heart hammer wildly against his chest. She rose up slowly, eyes flitting down to his lips and then once again locking onto his own. As if on instinct, Bellamy’s arm tried to close around her, but was held back by the knot that imprisoned him. When a desperate whine escaped from the back of his throat, O smiled, “you want me to kiss you?” she asked, her hand felt heavy on Bellamy’s naked chest as she stroked it idly- judging by the smirk she wore, she was clearly entertained by the turn of events. Without a word, Bellamy nodded, and his sister moved forward to seal her lips over his. 

He couldn’t help but melt against her as she experimented with his mouth. Her lips were soft, yet strong against his. Bellamy groaned when her warm hand slid from his chest to his waist and then under his boxers and wrapped around his painfully hard cock. He couldn’t stop groaning as his head fell back and O’s hand worked him faster and faster, _ “god, fuck-” _

“Bell, I want more than just your hands and your mouth… I want _you,_” she confessed, her thumb moving against the head of his cock, effectively smothering his arousal around, “I need you, big brother.” 

His hips worked against her movements as if they had a mind of their own. Although he knew he shouldn’t do it, he shouldn’t give in, he couldn’t help but imagine what it might feel like to be buried inside her- to be her first- and probably the only- lover she’d ever have. 

It was in that moment an undeniable fact dawned on Bellamy- there would never be another for her. Unless, by some miracle, she was discovered and allowed to live on the Ark. Considering how unlikely that is, as it stood… if he did this, he would be hers- and she would be his. 

If he didn’t do it, he’d still be hers- there was no way he could ever leave her or ever trust an Omega with their secret. 

Bellamy didn’t notice her hand coming up to untie his restraint until the first was released. Reacting quickly, he grasped her wrist before she could reach for the other, “what are you doing?” he growled, his voice sounding foreign to himself. 

“I want to let you out,” O said, her eyes wide as she registered the change in him, “I want you to fuck me, Alpha.” 

At that, Bellamy growled again. The word sounded delicious dripping from her lips, and he couldn’t help but grind against her leg that had fallen between his own. Without a word, Octavia’s lips dropped to his cheek. Slowly, carefully, she made her way to his jaw, his neck, his scent glands. Placing a small kiss there, O smiled and murmured against him, “If I mark you, you’ll be mine… then you have to make me yours, right?” 

_ “O,” _Bellamy warned, as her teeth grazed his skin lightly. Surprised, he sucked in a sharp breath just as she sunk her teeth into him. Then it all happened at once- an explosion inside of him- his hand moving to grip his sister’s hip, the sound of something popping- before he knew it, they were flipped over with O on her back, and Bellamy breathing frantically above her. 

In his periphery, Bellamy could see the torn rope- but right now, he couldn’t care less. As every inch of him burned with need, he pulled O's legs apart and hiked her dress up. As his hands moved to her underwear, he groaned- _she wasn’t wearing_ _any._

_"You planned this, didn't you?"_

Before she could say anything, he plunged his fingers into her. Pulling the dress up enough to get one of her nipples between his teeth, O let out a moan as his lips closed around her sensitive flesh. He licked, bit and sucked on her while she bit her hand to stifle her wild noises. 

When she was sufficiently wet, Bellamy pulled his fingers out and slowly plunged them into her mouth, letting her suck them off, as she would his cock. 

“This is your last chance to say no,” he offered. At that, she merely pressed her opening against his cock and wrapped her leg around his hip, likely in an attempt to get him to enter her, “just a moment, I can’t fuck you through my boxers, O,” Bellamy shook his head, laughing lightly. 

Pulling back, Bellamy turned her around, sat her up and pulled her dress off, “alright,” He said, getting his hands on her tits and playing with them, “I’m gonna do it this way, if it's too much, tell me.” 

O gave him a small nod, one of her hands playing with his curls and the other rubbing his thigh, “I’m ready, _Alpha,_” she said, teasing him with her husky voice. Slowly, Bellamy ran his hand down her back and pushed her forward. Carefully, he opened her legs and lined himself up with her. Just the sight of his massive cock splitting her open almost had him coming- but he couldn’t do that yet. He had to make this good for her, too. 

As he sheathed himself in her, O let out a desperate moan, yet she pressed herself against him, pulling him deeper and deeper into her warm, tight and pulsating cunt. Finally buried inside her, O sat back on his thighs and wiggled around in her brother’s lap. Tossing her head back onto Bellamy’s shoulder, she let out a moan and began to fuck herself on him. In awe of her, Bellamy watched until her breathing became erratic. Running his fingers down her body, he found her clit and gave her those little circles he knew she loved so much. 

O came with her lower lip between her teeth, one hand gripping his arm and the other delving into his curls. The more she shook, the harder he pressed against her clit- driving her wild, as she rose and fell on his cock. The tighter she got, the more difficult it became to control himself. As she came, his self-control waned and Bellamy found himself gripping her neck loosely as he held her up and fucked into her wildly. The more noise she made, the harder he fucked- until she was laying with her face in the pillows, moaning uncontrollably into them and he pounded into her over and over. 

Bellamy watched his body as it took every ounce of innocence from his sister. Leaning over her, he sunk his teeth into her neck. Of course, she had no scent glands there, but he couldn’t fight the instinct to mark her, to make her his as she had just done with him. Bellamy stilled as heat and pressure began to build at the base of his cock. 

Realizing it was his knot, he tried to pull out, but O tightened herself around him, _“no, don't-" _

_“Turn around, O,”_ he urged, helping to flip her over. Instead of sliding back into her, Bellamy slid his cock against her sensitive clit until they were both coming- O gasped as she rode out her second orgasm underneath him- and with his forehead against hers, he emptied his knot. 

Coming down from the high, Bellamy stared at his sister as she settled into his arms. With her head on his shoulder and her hand on his chest, a contented sigh escaped her lips. Planting a kiss on her forehead, Bellamy told her to get some sleep.

As she did just that, he laid awake and wondered exactly which circle of hell he might end up burning in. 

**Author's Note:**

> This was my first time writing Octavia and Belltavia... Let me know what you think!


End file.
